1. Field
Aspects of embodiments relate to a phosphor, a light emitting device, a surface light source device, a display device and an illumination device.
2. Description of the Related Art
In general, a phosphor wavelength conversion material has been used as a material converting light having a certain wavelength emitted by various light sources into light having a desired wavelength. In particular, among various light sources, light emitting diodes (LEDs) are able to be driven with low power consumption and have excellent light efficiency, and thus may be effectively applied to liquid crystal display (LCD) backlight units, vehicle lighting systems, and home lighting systems. Recently, phosphor materials have been recognized as a core technology in the manufacturing of white light emitting devices.
White light emitting devices have been generally manufactured in a scheme in which at least one or more types of phosphor, for example, a yellow or red phosphor and a blue phosphor, are applied to a blue or ultraviolet LED chip. In particular, when a red phosphor is combined with a different one or more types of phosphors to then be used, it may be difficult to secure a sufficient color rendering index in a case in which a full width at half maximum of a respective phosphor is relatively low, and there may be limitations in implementing desired natural white light. The color rendering properties required as above may be important evaluation terms when white light emitting devices are employed as light sources for illumination devices.
The white light emitting devices have been generally manufactured in a scheme of coating blue LEDs with yellow phosphors. In detail, light emission surfaces of blue LEDs having GaN/InGaN active layers are coated with yellow phosphors of YAG (Y3Al5O12):Ce to thus convert a portion of blue light into yellow, and converted yellow and a different portion of blue light are then combined to thereby provide white light. White light emitting devices according to the related art configured of the YAG:Ce phosphors (or TAG-based phosphors) and the blue LEDs as described above have relatively low color rendering properties. That is, since wavelengths of white light obtained using yellow phosphors are only distributed in blue and yellow and thus color rendering properties are relatively low, there are limitations in implementing desired natural white light. In addition, in the case of a silicate phosphor according to the related art, as a yellow phosphor, the phosphor is unstable with the application of heat and may thus be unsuitable to be used for high output LED chips.
In order to improve defects as above, α-SiAlON-based phosphors have been proposed, and α-SiAlON-based phosphors are known as being able to emit long wavelength light as compared to YAG:Ce phosphors (see Japanese Patent Laid-Open Publication No. 2002-363554 or the like). Such α-SiAlON-based phosphors have relatively excellent thermal stability, but have relatively low light emission efficiency as compared to that of YAG:Ce phosphors. Accordingly, a scheme for increasing light emission efficiency of α-SiAlON-based phosphors has been required.